Moore was the first to point out that carcinoma is more prevalent in the southern and eastern parts of England than in the northern and western districts ; and that if a line be drawn across the country from Bristol to Peterborough, the cancer mortality will be found to be much greater to the south than to the north of that boundary. At the present time the counties which present the highest death-rates from the disease are London, Cambridge, Huntingdon, Northampton, Sussex, Warwick, Bedford, Surrey, and Middlesex ; while those with the lowest are Derby, Bucks, Herts, Durham, Cornwall, Monmouth, Dorset, Lancaster, and parts of South Wales. These topographical variations in the cancer mortality would appear from estimates made by the Registrar-General to be independent of sex and age distribution. Another interesting fact that has been brought to light by investigations of this nature is that the death-rate from the disease is greater among rural than industrial populations, the inhabitants of country towns like Chichester, Canterbury, Huntingdon, and Cambridge being more affected than those of the great industrial cities. Haviland asserted that the highest cancer mortality is met with in lowlying districts which are traversed by sluggish streams and are liable to periodic inundations, and in support of this view he instanced the Thames and its tributaries, which run through districts that are markedly cancerous. That there is probably a good deal of truth in this contention is shown by the following remarks of the Registrar-General in his report for 1890 :-

'Crude death-rates show that in and around Huntingdonshire and Cambridgeshire there is a well-defined area in which cancer is exceptionally prevalent. It comprises the districts of Stamford, Bourn, Spalding, and Holbeach in Lincolnshire, Oundle and Peterborough in Northamptonshire, and most of the counties of Huntingdon and Cambridge. In 1881- 1890 this area had a mean population of over 300,000, its crude cancer-rate being 859 per million, or 46 per cent, above the average for the country in general; in the preceding decennium the excess was 44 per cent.' On the other hand, as Roger Williams has pointed out, many islands that have no rivers, that are not low-lying and are not of alluvial formation, such as the Scilly, the Channel Islands, and the Isle of Wight, have nevertheless a very high cancer mortality. In Norway also cancer occurs for the most part in the mountainous districts and at considerable elevations ; while in Mexico the high table-land is more subject to the disease than the lowlying plains (Hirsch). It follows, therefore, that whatever influence a special district may exert upon the development of cancer, geological configuration is by no means the sole factor in its production.

It has frequently been noticed that the inmates of certain houses are especially liable to carcinoma, which appears among successive tenants who are neither related to one another nor possess any hereditary predisposition to the disease (Arnaudet, Fabre, Webb, Fiessinger). In Webb's case a man died of cancer of the rectum in a certain house at the age of twentysix. Of the next tenants, the husband died of gastric cancer and the wife of cancer of the rectum ; while of the three ladies who next inhabited the house, one died from malignant disease of the stomach and another from a similar affection of the uterus. Mason has also shown that in the district of Leamington the disease is quite common in houses situated in certain rows or upon one side of a row, while in other streets it is conspicuous by its absence. This writer has also remarked that about 17 per cent, of these cancer houses were placed at the end or at the corner of a street, were of old construction, and were built upon a porous subsoil. In this connection it may be noted that both husband and wife not infrequently fall victims to carcinoma of the digestive organs if the survivor continues to reside in the same house, while occasionally the disease occurs almost simultaneously in both.!! Thus we have known a man to be attacked by cancer of the stomach while his wife was dying from a similar affection of the duodenum; and also a man and his two daughters to develop malignant disease of the stomach or colon within a period of twelve months. These several phenomena occur too frequently to be regarded as mere coincidences, and probably depend upon the operation of some well-defined local cause,'the nature of which, however, is still obscure.